1. Field of the Invention
This invention relates to the reduction of sulfur in gasoline produced in a fluid catalytic cracking process and, more particularly, to a method and composition for use in the fluid catalytic cracking process using a sulfur reduction additive composition.
2. Description of Related Art
Fluid catalytic cracking (FCC) is the largest refining process used for gasoline production with global capacity of more than 14.2 million barrels per day. The process converts heavy feedstocks such as vacuum distillates, residues, and deasphalted oil into lighter products, which are rich in olefins and aromatics. FCC catalysts are typically solid acids of fine-particles especially zeolites (synthetic Y-faujasite), aluminum silicate, treated clay (kaolin), bauxite, and silica-alumina. The zeolite content in commercial FCC catalysts is generally in the range of 5-40 weight %, or greater, while the balance is silica-alumina amorphous matrix. Additives to the FCC process usually amount to no more than 10% of the catalyst, and they are basically used to enhance octane, as metal passivators, SOx reducing agents, CO oxidation and, recently, for gasoline sulfur reduction.
Stringent environmental regulations that target the reduction of the sulfur content of automobile gasoline and tailpipe emissions are being enforced worldwide. Sulfur in gasoline increases SOx emissions in combustion gases, reduces the activity of vehicle catalytic converters, and promotes corrosion of engine parts. The upper limit of sulfur in gasoline in the United States and the European Union has been set at 10 parts per million (ppm) as a refinery average, and many other countries have also decreased the permitted sulfur specifications in transportation fuels.
A number of options are available for the reduction of sulfur in gasoline. The main options are hydrotreating the FCC feed, hydrotreating product naphtha, lowering the end boiling point of FCC gasoline, and the use of sulfur-reducing additives in FCC catalysts. The first two options are highly capital intensive. A disadvantage regarding the third option is that the lowering of end boiling point will also reduce the octane number, in addition to reducing the yield of gasoline. From an economic point of view, the last option is the most desirable since this will selectively desulfurize the gasoline fraction without the need for additional treatment. It has been reported that sulfur reduction by FCC additives or catalysts offers economic advantages over the standard solution-selective gasoline hydrotreating or hydrodesulfurization methods.
Various catalytic materials for effecting a sulfur reduction have been developed for use during the FCC process. The sulfur reduction component may be a separate additive to the FCC catalyst or part of an FCC sulfur reduction catalyst. However, the levels of sulfur in gasoline are still not low enough to meet current and proposed regulatory requirements and, accordingly, are unacceptable.
Catalyst additives for the reduction of sulfur in FCC gasoline products were proposed by Wormbecher in U.S. Pat. No. 5,376,608 and Kim in U.S. Pat. No. 5,525,210, the disclosures of which are incorporated by reference, using a cracking catalyst additive of an alumina-supported Lewis acid for the production of reduced-sulfur gasoline. It was also disclosed that the Lewis acid may comprise components and compounds including Zn, Cu, Ni, Ag, Cd and Ga deposited on aluminum oxide. However, this system has not achieved significant commercial success.
Another composition is that disclosed in U.S. Pat. No. 6,036,847 to Ziebarth et al., the disclosure of which is incorporated herein by reference, used 10 weight % of a mixture including particles of Zn supported on alumina and titania particles as an additive in the cracking of 2.7 weight % sulfur vacuum gas oil (VGO) feed. The results indicated that the combination of alumina-supported Lewis acid component and titania-containing component resulted in greater sulfur reduction than the use of either component alone.
Myrstad et al. in U.S. Pat. No. 6,497,811, the disclosure of which is incorporated herein by reference, disclosed a composition of a hydrotalcite material impregnated with a Lewis acid, and optionally an FCC-catalyst, as a sulfur-reducing additive. The Lewis acid included transition metals elements and compounds, including Zn, Cu, Ni, Co, Fe and Mn.
Another additive disclosed by Roberie et al. in U.S. Pat. No. 6,482,315, the disclosure of which is incorporated herein by reference, discloses a composition comprising vanadium supported on a refractory inorganic oxide. When using 2 weight % vanadium-containing additive, a 33% reduction in gasoline sulfur was reported.
Various papers, published by Andersson, P. et al., Catalysis Today 53:565 (1991), Beltran F. et al, Applied Catalysis Environmental 34:137 (2001) and 42: 145 (2003), relate in only a very general manner to the concept of the present invention.
Notwithstanding the reported sulfur-reducing catalysts, there remains a need for effective and economical catalysts for reducing sulfur from gasoline in a commercially sustainable manner.
Therefore, it is an object of the present invention to provide a sulfur-reducing composition and a method for the use of same which provides a gasoline with a significantly lower sulfur level, when compared to the sulfur reduction activity of a conventionally used FCC catalyst in the FCC process.